Technology
New waste recycling processes show promise European projects under way include conversion of scrap plastics and tires to gas, scrap tires to oil, and waste paper to high-grade oil Dermot A. O'SulliVan C&EN, London
Rubbish disposal is a critical and growing problem, especially in heavily populated areas. The job is becoming increasingly costly in terms of both energy consumption and sheer effort. West Europeans, like others elsewhere, are concerned about the issue. In Europe, attempts have been made with varying degrees of success to turn a social lemon into something of a lemonade. Indeed, the Commission of the European Communities is moving into the second phase of a four-year, $9 million research and development study program on the broad aspects of recycling urban and industrial waste. Meanwhile, three independent
projects are afoot that will make garbage a valuable asset, if they are as successful as their proponents believe they will be. Furthest along is one at Ingolstadt, near Munich, West Germany, where a commercial-scale plant is being built to convert scrap plastic and tires into gas and a variety of chemicals. It is due for startup early next year. At Wolverhampton in the U.K., about 15 miles from Birmingham, a somewhat similar plant is planned for completion in 1984. This plant will reduce scrap tires to oil. And at England's University of Manchester Institute of Science & Technology (UMIST), a study currently is under way toward producing high-grade oil from waste paper and other cellulosic materials. The Ingolstadt and Wolverhampton plants will use pyrolysis technology. UMIST uses autoclaving. The Ingolstadt operation belongs to Deutsche Reifen- und Kunststoffpyrolyse (DRP), the West German Tire & Plastics Pyrolysis Co., wholly owned by C. R. Eckelmann, a Hamburg-based concern engaged in container terminaling. DRP will have two pyrolysis units. The larger will be capable of burning bulk plastic and
Hamburg process pyrolyzes whole tires and plastics Waste
Cyclone
Cooler
Oil Fluidized-bed reactor
Exhaust gas Carbon black Water Excess gas Steam Distillation Compressor
iSand^ Air
Gas
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C&EN April 12, 1982
complete tires. The other will be used for smaller pieces of plastic, such as shredded waste and film. Together, they will be capable of treating upward to 22 million lb of waste each year. The installation will cost about $5 million, funded partly by the West German Ministry of Research & Technology. The plants will be scaled-up versions of pilot units engineered by Walter Kaminsky and Hansjôrg Sinn at the University of Hamburg's Institute of Inorganic & Applied Chemistry. Their pyrolysis studies, under way since 1970, have been supported by the West German Plastics Industry Association as well as by the research and technology ministry. Bulk waste plastic enters at the top of the pyrolysis furnace through twin hoppers. Whole tires are rolled through a specially designed gas-tight lock feeder system. In the case of small plastic pieces and film, it's best to introduce the waste directly into the body of the fluidized bed. Otherwise, Kaminsky observes, turbulent currents tend to keep them suspended high on the walls above the reaction zone. The fluidized bed itself is of quartz sand with a grain size ranging between 0.2 and 0.5 mm. Recycled hot pyrolysis gas, introduced through jets at the base of the furnace, serves as eddy gas. Pyrolysis gas, which has a calorific value of between 40 and 50 megajoules per cubic meter, also is fed to burners extending into the body of the sand that maintain the furnace temperature at about 800 °C. The burners are designed so that exhaust gases don't enter and contaminate the fluidized bed. Residence time of waste in the furnace is short. Plastics vaporize and decompose almost instantaneously. Whole tires are consumed in five minutes or less. Hot gases leaving the furnace pass first to a cyclone where carbon black and any other entrained solids separate. The gases then go through a heat exchanger for cooling, and on to a distillation unit. Uncondensed gas is recycled back to the reactor. On average, 100 lb of plastic results in 2 lb of carbon black and 2 lb of tar. About half of the 96 lb of hot gas is
liquefied. On distillation, this yields benzene (50%), toluene (10%), xylenes (5%), and naphthalene (10%). The remaining 25% or so consists of a mixture of cyclopentadiene unsaturated polycyclic aromatics. Main components of the gaseous fraction are methane (about 40% by volume), ethylene (30%), and hydrogen (20%). The remainder is a mixture of carbon monoxide, carbon dioxide, water, and aliphatics. The important aspect of the operation, Kaminsky stresses, is that it is self-supporting in terms of energy requirements. Moreover, surplus gas produced could be used for heating buildings in the neighborhood of the reactor. Also, recovered carbon black, as well as the tar and aromatics, has a possible commercial value. Early in their studies, the Hamburg workers elected to pyrolyze complete tires. This avoids the time-consuming job of preshredding them, a task made more difficult with the growing quantities of discarded steel radiais. It was due largely to the problem and expense encountered in shredding such tires that Goodyear Tire and Oil Shale Corp. (Tosco) elected to abandon a joint pilot project aimed at pyrolyzing scrap tires (C&EN, June 10, 1974, page 5). Such experience doesn't appear to have discouraged participants in the Wolverhampton, U.K., tire pyrolysis scheme. The $11 million plant will be capable of pyrolyzing 110 million lb a year of scrap tire rubber. Annual output will come to 44 million lb of light fuel oil with a calorific value of 43,000 megajoules per ton. In addition, there will be 37 million lb of friable char suitable for fuel, and 15 million lb of steel scrap. Gas that's generated will provide energy for the process. The owner of the operation is Tyrolysis, set up earlier this year. Foster Wheeler Power Products and Leigh Industries, a specialist in high-technology waste treatment in Walsall, near Wolverhampton, are the chief participants in the new company. Foster Wheeler has acquired ownership of the technology, which was developed at the U.K. Department of Industry's Warren Spring Laboratory in Stevenage, near London. At UMIST, Roger Benn and Noel McAuliffe elected to concentrate on the high-pressure approach to converting cellulosic waste matter to oil, "because that basically is the way oil has been formed in nature," they observe. " We also had the advantage of having at hand a number of highpressure test reactors."
UMIST researchers Roger Benn and Noel McAuliffe work on their 30-L stainless steel autoclave that converts waste cellulosic materials to oil
When they subject a slurry of cellulosics in a hydrocarbon solvent and in the presence of metal catalyst to 100 atm pressure and heat it to about 350 °C, heavy viscous oil is formed. This has a calorific value of some 40,000 megajoules per ton, "equivalent to good-quality Middle Eastern crude," they point out. Equally attractive, from a practical viewpoint, is that the product contains neither nitrogen nor sulfur, and therefore is nonpolluting. Residence time in the autoclave is about five minutes. No external source of hydrogen is needed, as Benn and McAuliffe had expected there would be in the early stage of the study. Seemingly, the reducing species needed to strip oxygen from the cleaved cellulose chains are gen-
University of Hamburg's Walter Kaminsky and pyrolysis pilot unit
erated in situ under the combined influence of the catalyst and solvent, both of which are recoverable. During the past three years or so, the UMIST workers have been running batch experiments. More recently, they have used a 30-L stainless steel vessel fitted with a magnetically operated agitator. This is being converted to operate continuously. There is no shortage of feedstock. Waste material is supplied by Greater Manchester County, which has funded the work through Salford University Industrial Center. Following the forthcoming series of continuous test runs, the next step will be to consider scaling up the equipment. Preliminary calculation suggests that a plant capable of handling 2.2 million lb daily of cellulosic refuse would cost about $36 million. Such a facility would have an oil output of about 3000 barrels per day. The plant could be paid for within five years if the oil were priced at $15 per bbl. McAuliffe admits that it isn't easy at this point to put a retail value on the oil. But he maintains that it certainly would be well below current oil prices, even at their presently depressed level. He and Roger Benn see a broader implication to their development. They are confident that the technique can be used with a variety of alternate biomass cellulosic feed. Typical feedstocks would be bagasse, cassava, corn husks, and even grass. Hamburg University's Kaminsky, too, has an eye on biomass as feedstocks for his pyrolysis technology. He plans test runs with sawdust, wood chips, and, eventually, sewage sludge. D April 12, 1982 C&EN
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